This invention relates to a motion detector and particularly to such a detector for incorporation into an electronic device which detects movement of an individual carrying the device.
As a means of increasing the convenience of entering a locked motor vehicle, many designs for so-called keyless entry systems have been proposed. Such systems would enable the vehicle to be unlocked without requiring the user to employ a conventional key-type locking system. One approach is to provide an external keypad on the motor vehicle through which the user inputs a code to unlock the vehicle. Although such systems eliminate the need for using a conventional key, they nonetheless require the user to take time to manually input the code before being able to enter the vehicle.
Another approach is to provide an electronic device carried by the user which can be activated when in close proximity to the vehicle to emit a coded signal which is processed by a receiver in the vehicle to unlock the vehicle. The transmitter/beacon device carried by the user could be activated by a pushbutton or other means. In order to provide a totally passive keyless entry system, the transmitter could be controlled to emit a unique coded signal on a continuous basis. Although this approach is advantageous in that no action is required by the user, it could lead to unacceptable high drain of the internal power source of the transmitter. In order to converse battery drainage, a motion detector can be incorporated into the transmitter which senses movement such as occurs when an individual is walking toward their vehicle. The motion signal is then used to activate the transmitter causing it to emit its coded signal. When the transmitter and its internal motion detector are at rest. for example, when the user having the device is sitting quietly or while it is stored temporarily, the transmitting circuit can be turned to an off or quiescent state thereby eliminating or reducing battery drain to the micropower range. In order for such a motion detector to perform satisfactory, it must detect extremely low levels of acceleration in all orientations as would be expected when a user is carrying the transmitter in their pocket. Moreover, such a motion detector should be easy to assemble, employ few parts, and feature low cost materials and construction.
A motion detector achieving the above-mentioned desirable features is provided according to this invention. The motion detector includes a spool-shaped conductor which is surrounded in a clearance relationship by a cylindrical conductive shell. A conductive ball is trapped within the annular space around the spool. When the ball is moved into and out of contact with the spool and shell, an interrupted electric signal is provided which signals movement. In addition, one or more of the contacting surfaces of the motion detector can be intentionally roughened so that movement of the ball while remaining in physical contact with the two electrodes will cause an interrupted current condition through the switch which is interpreted as movement. Both the spool and outer cylindrical shell can be mounted directly to a printed circuit (PC) board for convenient mounting and assembly.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.